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​Forestry: Insect Risks

Insect herbivores and pathogens can cause productivity and value loss and forest degradation. Climate change, primarily changes in temperature and precipitation, can enhance the disturbance caused by insects and pathogens through direct impacts on their growth and development, namely enhancing survival, reproduction and dispersal.

Effects can be increased or offset by changes in the growth and development of natural predators, mutualist insects or pathogens and competitors that currently constrain populations.

A typical climate change response predicted is an increase in suitable habitats. Published studies predict changes in species distribution in response to climate change.

Empirical relationships can be used to predict a range expansion or reduction under different climatic conditions by defining the current climatic envelope of a species and identifying the new geographic extent based on changes of climate variables under climate change.

Pine processionary moth

The distribution of the pine processionary moth has been projected using a niche climate model – Climex.

With the current climate, 60% of the total New Zealand radiata plantation area was found to be suitable for the moth, whereas under future modelled climate the geographic range was projected to extend to 93% of the radiata plantation estate.

The productivity impacts, under current climate, of the moth establishing itself in New Zealand are an average volume reduction of 16% over the course of a rotation. Estimated reductions in productivity range from 42.5% in Northland to 0% in many South Island regions, with losses (NPV) estimated at NZ$1.3 billion. With lower rates of dispersal, NPV losses ranged from between NZ$167 million to $500 million.

Under future climate the projected reductions in average volume for all of New Zealand ranged from 29% to 33% between different climate scenarios. The losses (NPV) ranged from NZ$2239 million to NZ$2493 million.

Statistical models and field translocation experiments show that range expansion will occur with increases in temperature.

Changes in temperature can cause early season effects on phenology; while range expansion was related to rises in average winter temperatures.

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